This invention relates to improved unsaturated polyester resin molding compounds (compositions) and particularly to improved cold-setting and thermosetting unsaturated polyester resin molding compounds.
In the manufacture of molded articles from such molding compounds, certain properties have been found to be desirable. Thus, thermosetting molding compounds should set shrinkage-free, i.e., shrink-free, and cold-setting molding compounds should set with low-shrinkage, i.e., they should exhibit an antishrink effect or LP effect. As used herein the term LP (low profile) refers to EP-OS No. 0 028 841, page 2, lines 8 to 31, and DE-OS No. 34 26 425, page 4, lines 5 to 10.
The set molded articles should also exhibit good mechanical properties, especially good elasticity, and a flawless surface, measured in terms of surface smoothness, and surface luster.
The unsaturated polyester resin, containing saturated polyester as LP additive, on which the molding compounds are based, and the molding compounds must not separate during storage under ordinary conditions e.g., ordinary conditions of temperature and time or, in the case of cold-setting molding compounds, potlife. In case of separation, the LP effect generally decreases to unacceptable levels or is lost entirely. Even if the resin and the molding compounds do not separate during storage, the LP effect can still decrease to unacceptable levels or be lost due to LP drift. This also should be avoided.
DE-OS No. 34 26 425 discloses unsaturated polyester resins and molding compounds obtained therefrom, which meet such requirements. However, the resins contain a combination of two types of LP additives, i.e., a thermoplastic polymer in addition to a saturated polyester. Their use is comparatively expensive from a commercial standpoint, e.g., they require expensive warehousing and processing considerations, e.g., expensive mixing procedures, etc.